( ( (Surround Sound ) ) ) Through the Stages© Asif Iqbal
Jun 17, 2001
The first commercially successful multi-channel sound formats were developed in the early 1950s for the cinema. At the time the film industry was threatened by the rapid advancement & expansion of television. The film industry, in multi-channel stereophonic sound, saw an opportunity to pull the masses back to its fold. Film stereo started out with a minimum of four channels sometimes going up to eight channels, unlike the two-channel format currently used for home stereos. Multiple sound channels were recorded on stripes of magnetic material applied to each print released for cinemas. Specialized projectors fitted with playback heads (much like your home tape recorder) were used to play these prints. Cinema halls were equipped with sound amplifier and speaker systems to get the desired effect. Film stereo, right from the beginning consisted of several channels across the front and at least one channels towards the rear or side of the audience. This rear channel was called the “effects channel” and used to play only occasional special effects such as heavenly voices. The problem with this sound setup was its costs. The multi-channel sounds were recorded on expensive magnetic tapes. Experiments with the new sound system continued nevertheless the effects channel was used to create greater realistic sound overall and was not restricted to the occasional dramatic effect as it previously was. This came to be known as surround sound, and thus the effects channel was renamed the “surround channel”. When stereo came into the home it came with only two channels. This was because two channels (left and right) were all that the then-prevalent system could accommodate. Two-channel stereo music reproduction was an amazing advance over mono sound systems. A few years later two-channel stereo FM broadcasting was introduced and made two channels synonymous with surround sound. As home stereo grew in popularity, equipment manufacturers began look for ways to expand their market. Since all home equipment currently in the market was based on two channel systems, the obvious idea was to somehow cram more data into the existing channels so that the total data could be divided into four channels played from four separate speakers. This lead to the four-channel, or quadraphonic (“quad”), home stereo format promoted in the early 1970s. This required two additional speakers placed at the rear of the listener to play all the four channels embedded into the source. Several schemes were developed to encode the basic two channels with additional sound information, based on the matrixing techniques these schemes were able to fold extra channels into the two regular channels by recording them with different relative phase. The problem that arose was that several encoding systems were designed and most were not essentially compatible with each other.
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